New groups of rotaviruses which are antigenically distinct form previously recognized rotaviruses have recently been reported as etiologic agents of gastroenteritis in animals and man. One group of these antigenically distinct rotaviruses, the group B rotaviruses, may be particularly pathogenic for humans. A strain of group B rotaviruses (GBR) has been isolated from rats and humans in Baltimore, Maryland, and different strain of GBR has been associated with large outbreaks of diarrhea among humans in China. However, the clinical significance of these viruses as human pathogens in the USA has not been determined and their molecular structure remains undefined. We have recently identified the infant rat as a useful model for GBR infection. We propose to isolate GBR from this source and from infected gnotobiotic calves in order to investigate the structural and antigenic relatedness of GBR strains to each other and to group A rotaviruses. GBR gene coding assignments will be identified by in vitro translation of viral RNA, and the presence of group-specific and neutralization antigens will be assessed by generation of monoclonal antibodies. Genes identified as containing these important antigenic sites will be selected for synthesis of full-length cDNA clones. These clones will then be used to investigate the genetic relatedness of human and animal strains of GBR by hybridization and nucleic acid sequence techniques. In order to isolate individual GBR proteins for study of protein structure and function, we will transfect eukaryotic cells with plasmid vectors containing cDNA clones of GBR genes hybridized with regulatory sequences of the simian cytomegalovirus. Diagnostic assays for the detection of GBR will also developed from clones of the viral genome and from monoclonal antibodies to viral antigens. These assays will then be used in order to evaluate the epidemiology of GBR infection and the clinical significance of the Baltimore strain of GBR for human disease. The infant rat model of GBR infection will also be employed to investigate the mechanisms by which the virus infects host cells as well as to define antigenic epitopes involved in viral neutralization. The results of these studies will permit the evaluation of GBR as candidates for inclusion in the current efforts to develop a human rotavirus vaccine. The experimental results should also aid in designing strategies to prevent and treat rotavirus infections.